Since the hydrolysis of a compound having an ester bond such as a polyester is promoted by a polar group such as a carboxyl group, it is proposed to reduce the concentration of the carboxyl group by using a sealing agent for a carboxyl group (Patent Document 1, Patent Document 2). A carbodiimide compound is used as the sealing agent for a carboxyl group.
However, since this carbodiimide compound is a linear compound, a volatile isocyanate compound is by-produced during use and generates a bad odor, thereby deteriorating work environment.
Then, the inventors of the present invention found as the sealing agent a cyclic carbodiimide compound which does not by-produce an isocyanate compound when it reacts with a carboxyl group and filed an international application (Patent Document 3). However, industrial processes for producing this useful cyclic carbodiimide compound and an intermediate therefor have not been established.    (Patent Document 1) JP-A 2004-332166    (Patent Document 2) JP-A 2005-350829    (Patent Document 3) PCT/JP2009/071190